Systemic hypovolemia and hypotension increase plasma renin activity (PRA) in fowl, but it is not clear whether this response is mediated directly by reduced renal arterial perfusion pressure (RAPP) or indirectly via renal nerves activated when systemic baroreceptors detect hypotension. To evaluate the influence of RAPP on renin release, arterial and renal venous blood samples were collected as RAPP was reduced step-wise from 108 mm Hg (control) to 71 and 47 mm Hg. PRA in systemic arterial (aPRA) and renal venous (vPRA) plasma was measured as the rate of fowl angiotensin I (ANG I) generation. Basal vPRA (2.47 +/- 0.6 ng x ml-1 x min-1) tended to be higher than aPRA (1.24 +/- 0.3 ng x ml-1 x min-1). When RAPP was reduced to 47 mm Hg both vPRA (4.35 +/- 0.6 ng x ml-1 x min-1) and aPRA (1.91 +/- 0.3 ng x ml-1 x min-1) increased significantly. Significant negative slopes (P = 0.01) were obtained when changes in aPRA or vPRA were regressed on RAPP. Mean systemic arterial pressure did not change during reductions in RAPP, nor did angiotensinogen concentrations differ when systemic arterial (472 +/- 30 ng/ml) and renal venous (460 +/- 27 ng/ml) plasma values were compared. Renal plasma flow was fully autoregulated as RAPP was reduced from 108 to 47 mm Hg; consequently, RAPP-induced increases in vPRA cannot be attributed to hemoconcentration of secreted renin. These results demonstrate that reductions in RAPP directly stimulate renin release from domestic fowl kidneys.